1. Field of the Invention
The present invention relates to earth-boring drill bits and methods of fabricating such bits and the components thereof. Particularly, the present invention relates to the controlled deposition and affixation of layers of one or more material employed as a matrix material of the bit or bit component, which is also referred to as xe2x80x9clayered manufacturingxe2x80x9d. More particularly, the present invention relates to methods of fabricating a substantially hollow shell of a component of a drill bit, such as a bit crown or other article of manufacture, comprising disposing the substantially hollow shell adjacent a cavity of a mold, disposing a material within the substantially hollow shell and within the cavity of the mold, and infiltrating the shell.
2. Background of Related Art
Earth-boring drill bits that include fixed cutting elements on the face thereof, which are commonly termed rotary drag bits or simply drag bits, typically include a bit body formed of steel or fabricated from an infiltrated matrix of a hard, particulate material, such as tungsten carbide. Particulate-based bit bodies are typically infiltrated with infiltrants, or binder materials, such as copper alloys. The bit body of a drag bit is typically secured to a steel shank. The steel shank typically includes a conventional American Petroleum Institute (API) threaded pin connection by which the drill bit may be secured to the drive shaft of a downhole motor or a drill collar at the distal end of a drill string.
Conventionally, steel bodied bits have been machined from round stock to a desired shape, with topographical features and internal watercourses for delivering drilling fluid to the bit face. Hard-facing may then be applied to the bit face and other critical areas of the surface of the bit, and cutting elements secured to the face of the bit. A shank may be machined and threaded on the drill bit.
In the conventional manufacture of a particulate-based drill bit, a mold, including inserts therefor, is milled or machined to define the exterior surface features of the drill bit. Typically, after a first milling of a block of mold material, such as graphite, to define a mold cavity that will subsequently define larger topographical features of the drill bit, a secondary milling is required to define cutter pockets and side supports therefor on the face of the drill bit. Additional hand milling or clay work may also be required to create or refine topographical features of the drill bit.
Once the mold has been milled or otherwise machined, a preformed bit blank of steel or other suitable material may be disposed within the mold cavity to internally reinforce the bit body matrix upon fabrication of the bit body. Inserts, such as performs that define internal fluid courses, pockets for cutting elements, ridges, lands, nozzle displacements, junk slots, or other topographical features of the bit body, are also inserted into the cavity of the mold. The performs must be individually designed and fabricated, and even minor changes in a drill bit design may necessitate the use of new and different performs. The performs must be placed at precise locations within the mold to ensure the proper placement of cutting elements, nozzles, junk slots, etc.
A quantity of particulate-based material may then be disposed within the cavity of the mold to define a bit body matrix. The bit body matrix is then infiltrated with a molten metal infiltrant to form a solid bit body after solidification of the metal infiltrant and to secure the preformed bit blank to the bit body.
The bit body may then be assembled with other drill bit components. For example, a threaded shank is then welded or otherwise secured to the blank and cutting elements (typically diamond, and most often a synthetic polycrystalline diamond compact or PDC) are secured within the cutting element pockets, such as by brazing, adhesive bonding, or mechanical affixation. Alternatively, the cutting elements may be bonded to the face of the bit body during furnacing and infiltration thereof if thermally stable PDC""s, commonly termed TSP""s, are employed.
Accordingly, the process of fabricating a particulate-based drill bit is a somewhat timely, costly, and complex process that requires the labor-intensive production of an intermediate product (the mold) before the end product (the bit body) can be cast.
In some cases, the mold fabrication process has been made faster and less costly through the use of rubber displacements, which duplicate, in fine detail, the topography of an entire bit profile and face. These displacements are used to cast a ceramic bit mold having an appropriate interior configuration, from which a bit may be cast. Typically, however, such rubber displacements may only be employed in the fabrication of xe2x80x9cstandardxe2x80x9d bits, which are fixed in design as to the size, number, and placement of cutting elements and as to the size, number, and placement of nozzles. Thus, rubber displacements are only cost-effective for fabricating high-volume drill bits, of which there are relatively few. With frequent advances and changes in bit design, preferences of individual customers for whom bits are fabricated, and the general decline in the number of wells being drilled in recent years, high-volume standard bits have become almost nonexistent.
Layered-manufacturing processes, such as those disclosed in U.S. Pat. No. 5,433,280 (hereinafter xe2x80x9cthe ""280 Patentxe2x80x9d), issued to Smith on Jul. 18, 1995, and in U.S. Pat. No. 5,544,550 (hereinafter xe2x80x9cthe ""550 Patentxe2x80x9d), issued to Smith on Aug. 13, 1996, both of which are assigned to the assignee of the present invention and incorporated herein in their entireties by this reference for all purposes, were originally intended to reduce the cost and time required to fabricate particulate-based bit bodies.
The ""280 and ""550 Patents disclose a method of fabricating a bit body, drill bit component, or other article of manufacture in a series of sequentially superimposed layers or slices. As disclosed, a drill bit is designed as a three-dimensional xe2x80x9csolidxe2x80x9d model using a computer-aided design (CAD) program, which allows the designer to size, configure and place all internal and external features of the bit, such as (by way of example) internal fluid passages and bit blank voids, and the rakes and locations of external cutting element pockets, as well as the height, thickness, profile and orientation of lands and ridges on the bit face, and the orientation, depth and profile of waterways on the bit face and junk slots on the bit gage. The CAD program then provides a xe2x80x9c.STLxe2x80x9d file (i.e., a file which represents the surface of the bit body), which may later be transformed into a solid model and numerically xe2x80x9cslicedxe2x80x9d into a large number of thin, planar layers by known processes employing known computer programs.
After the mathematical slicing or layering is preformed, a horizontal platen is provided on which a granular or particulate material such as a tungsten carbide coated with a laser-reactive bonding agent, such as a polymer, a resin, and/or a low melting point metal such as Wood""s metal or a lead alloy, or tungsten carbide intermixed with such a laser-reactive bonding agent is deposited in a thin, uniform layer. A finely focused laser, a focused light source such as from an incandescent or discharge type of lamp, or other energy beam, programmed to follow the configuration of the exposed section or layer of the bit body, is directed on the powder layer to melt the bonding agent and bond the metal particles together in the areas of the layer represented as solid portions of the bit in the model. Another layer of powder is then substantially uniformly deposited over the first, now-bonded layer, after which the metal particles of the second layer are bonded simultaneously to each other and to the first, or previously fabricated, layer by the laser. The process continues until all layers or slices of the bit, as represented by the solid model, have been deposited and bonded, resulting in a mass of bonded-particulate material comprising a bit body which substantially faithfully depicts the solid computer model in every dimensional respect. In areas of each layer that do not form a part of the completed article, the laser or other energy beam does not traverse and bond the particles. Thus, a drill bit, or at least a bit body comprised of bonded-particulate material, may be fabricated directly from the CAD-generated solid model without the necessity of designing and fabricating molds, and without the delicate, artistic hand labor required to define a cavity with the fine details of the topography of the face of a drill bit.
In a variation of the layered-manufacturing process, a tungsten carbide or other suitable powder or mix of powders (either metallic or nonmetallic) having the desired physical characteristics for a matrix may be uniformly premixed with a powdered binder, such as a metallic or nonmetallic (e.g., polymeric) binder powder, the premix deposited in layers, and the binder powder at least partially fused by a laser to bond the tungsten carbide particles into a matrix and define the bit body shape. After the layered-manufacturing process is completed, since the binder is already in place, the bit body may be heated to effect complete in situ infiltration of the matrix. Alternatively, layers of binder powder and matrix powder may be alternately deposited. In either case, additional binder may be placed on top of the bit body to infiltrate and fill any voids in the binder-consolidated metal powder matrix.
In another variation of the bit body layered-manufacturing process, a binder-coated matrix material (e.g., tungsten carbide) may be dispersed into a layer, and the binder coating melted with a laser sufficiently to cohere the particles of each layer and adjacent layers to one another. The bit body may then be heated to complete the in situ infiltration of the matrix. Additional binder may also be employed, as noted above.
In yet another variation of the bit body layered-manufacturing process, particulate material is dispersed into a layer, and the particles in selected areas of the layer affixed to one another by a polymeric adhesive or non-polymeric binder (e.g., water-glass). Due to the selective deposition of binder over the layer of particulate material in order to define a desired solid structure, this type of layered-manufacturing is typically referred to as xe2x80x9c3D-Printingxe2x80x9d.
The bit body may then be placed in a furnace where it may be preheated to substantially remove the bonding agent. In such instances, certain metal powders may be at least preliminarily sintered or fused, such sintering to be enhanced or completed, if necessary, in a later furnacing operation.
If a powdered metal coated with bonding agent or metal intermixed with bonding agent is employed as the particulate material as mentioned above, the resulting bit body is a porous and permeable metal mass akin to a sponge or an open-celled foam, which can be imbibed with suitable hardenable infiltrants, either metallic, non-metallic, or a combination thereof, to complete the bit body. If an infiltrant in liquid form at room temperature (e.g., certain polymers) is employed, the bit may be mass infiltrated via capillary action, gravity, and/or pressurized flow at room temperature. If an infiltrant that is solid at room temperature is employed, the bit may be mass infiltrated by capillary action, gravity, and/or pressurized flow while the infiltrant is heated, such as by a furnace or an induction coil.
The infiltration process may include pouring a castable material able to withstand the high temperatures typically encountered during the infiltration process, such as ceramic, plaster, or a graphite slurry, around the particulate-based bit body or assembly to provide solid structure support upon solidification or hardening of the castable material. Similarly, the bit body or assembly may be dipped one or more times into a castable material, such as a ceramic, plaster, or graphite slurry, to form a relatively rigid material around the bit body. In either case, any orifices or openings leading to internal passageways in the bit body may be plugged prior to casting so that castable material that may otherwise be difficult to remove therefrom does not accumulate inside the bit body or assembly. Materials such as sand, graphite particles, and clay may be employed to plug these orifices or openings.
Alternatively, the particulate-based bit body or assembly may be placed in a refractory vessel with granular material packed around the particulate-based bit body up to its uppermost surface. This granular material substantially completely surrounds all surfaces of the bit body and may be vibrated to more densely pack the granular material. Because the granular material maintains its granular form during infiltration and is nonwettable by the infiltrant, the granular material effectively forms a xe2x80x9cconformingxe2x80x9d mold. That is, the granular material continues to provide structural support for the bit body during infiltration, even as dimensions of the bit body change, such as by expansion and shrinkage that may occur as bonding agent employed to preliminarily hold the metallic particles of the bit body together melts or vaporizes. The granular material may not substantially sinter, tack, or otherwise strengthen during the infiltration process so as to avoid complicating its removal from the bit body following infiltration, and thus continues to support the bit body substantially throughout infiltration without substantial change in its supporting physical characteristics.
A granular material that sinters, chemically reacts, or otherwise strengthens during the infiltration process may be used with bit bodies that undergo little or no shrinkage during infiltration in order to provide a more rigid mold to support the bit body. Substantially rigid molds may also be employed to provide support primarily during the first stages of infiltration, wherein the metallic particles of the layered bit body are imbibed with a sufficient amount of infiltrant and/or sufficiently sintered so that the bit body can structurally support itself.
Mold materials are typically selected to conform by shrinking and/or expanding along with any shrinkage and/or expansion of the bit body during the infiltration process and, thus, to maintain a substantially impermeable, conforming support structure during infiltration. These molds may also prevent infiltrant from flowing out of the bit body and pooling in gaps that may otherwise form between the bit body and the interior surface of a mold having dimensions that do not vary with the varying dimensions of the bit body during infiltration.
Typically, the materials used to form the support structure and/or fill any internal cavities in the bit body are non-wettable by the infiltrant. That is, these materials do not absorb or otherwise chemically or mechanically bond to or react with the infiltrant. Rather, because of their non-wettable quality, these materials form a barrier around the bit body so as to contain the infiltrant within the bit body and to prevent the support structure from binding to the bit body. In addition, such molds or support structures may be formed from materials that are substantially permeable to gases and vapors generated during the infiltration process, so as to preclude the formation or retention of gas- or vapor-created voids between the mold and the bit body during infiltration.
If a wettable material is used to form the support structure, the bit body may be coated with an infiltrant-resistive material, such as boron nitride, water-glass, or other suitable materials known in the art, prior to being placed within, or surrounded by, the support material. The boron nitride may be simply sprayed or painted onto various surfaces of the bit body, or the bit body may be dipped into a container of a boron nitride suspension to form a barrier through which the infiltrant cannot flow out of the bit body and imbibe the wettable support structure. Thus, the non-wettable and impermeable (by the infiltrant) resistive coating keeps the molten infiltrant contained within the layered bit body. In addition, such a coating may aid in forming a better surface finish for the bit body as it creates an intermediate shell to which the layered part and the infiltrant can conform during infiltration. Moreover, due to its liquid consistency, the coating fills small voids, vugs or intricately configured areas that may not be completely, intimately contacted by the surrounding support material. During the coating process, it is generally desirable to leave at least one surface uncoated so that the bit body has at least one non-resistive, or wettable, surface through which to imbibe additional infiltrant, even if infiltrant is already present in the preformed particulate-based bit body. Such a resistive coating may also be used in conjunction with variations of the infiltration process, whether the support material is wettable or non-wettable, to help form a better surface finish and help ensure that the infiltrant does not flow out of the particulate-based bit body and into the support structure, pool in any voids, gaps or vugs present between the bit body and the support structure, or form an unwanted skin of infiltrant on the outer surface of the bit body.
After the particulate-based bit body has been properly supported, the bit body and any supporting materials and/or structures are placed within a traditional furnace, an induction coil furnace, or other heating apparatus along with an infiltrant and heated until the infiltrant melts and substantially permeates the bit body through the free, or uncoated, surface exposed to the infiltrant. The materials that have been conventionally employed to infiltrate particulate-based bit bodies include copper-based alloys that include other elements, such as nickel.
The ""280 Patent and the ""550 Patent also disclose a tungsten carbide or other suitable powder or mix of powders (either metallic or non-metallic) having desired physical characteristics for a matrix substantially uniformly premixed with a powdered polymeric (or other nonmetallic) or metallic infiltrant powder, the premix deposited in layers and the infiltrant powder at least partially fused by a laser to bond the tungsten carbide particles into a matrix and define the bit body shape. After the layering and fusing process is completed, since the infiltrant is already in place, the bit body is heated in a furnace to effect complete in situ infiltration of the matrix. In another alternative to the foregoing procedure, layers of matrix powder alternating with layers of infiltrant powder are deposited. In either case, additional infiltrant may be added during infiltration to fill any infiltrant-deprived voids in the infiltrant-consolidated metal powder matrix. If an infiltrant-coated tungsten carbide or other suitable powder or mix of powders in a layered fashion is employed, a laser may be used to melt the infiltrant coating at least enough to cohere each layer, and the completed bit body placed in a furnace for an in situ infiltration of the bit body, with additional infiltrant being provided if necessary, as noted above.
A support structure may also be employed to infiltrate a bit body comprised of metallic particles intermixed with particles of an infiltrant material. With such a particulate-based bit body, it may not be necessary to leave at least one surface exposed for additional infiltrant to be imbibed into the bit body. Such a particulate-based bit body may, however, require structural support as described above.
While matrix-type bits may offer significant advantages over prior art steel body bits in terms of abrasion- and erosion-resistance, and while recent advances in matrix technology have markedly increased the toughness and ductility of matrix bodies, in many cases, the cost of a matrix-type bit and the time to fabricate same may result in the customer choosing a cheaper steel body bit with a faster delivery time. In either case, the customer must choose between a tough but less abrasion-resistant bit and a more expensive, highly abrasion- and erosion-resistant bit with reduced toughness.
Accordingly, it would be advantageous to provide a process of fabricating a drill bit, drill bit component, or other article of manufacture in less time, with less cost, and without sacrificing the orientation, alignment, and detail of the various features of the article of manufacture.
The method of the present invention includes employing known layered-manufacturing processes to fabricate a particulate-based, substantially hollow shell of a crown of a bit body, positioning a bit gage mold adjacent the substantially hollow shell, and disposing a core material, which may also be referred to herein as a bit material, within the substantially hollow shell and the bit gage mold to form a mold interior and a bit gage. The core material may be either a molten material or a particulate-based material.
The method of the present invention may also include infiltrating the substantially hollow shell and/or the core material (if the core material is particulate-based) with a binder, which is also referred to herein as an infiltrant. The method may further include disposing the substantially hollow shell within a soft, or conforming, mold material to support the substantially hollow shell during disposal of the core material within the substantially hollow shell and the bit gage mold. Preferably, the material of the soft, conforming section of the mold is a non-wettable material that substantially conforms to the exterior surface features of the bit crown and that prevents molten material from flowing substantially past the exterior surfaces of the bit crown.
Since, according to the method of the present invention, the bit crown is fabricated prior to fabrication of the interior and gage of the bit, the bit crown may be fabricated from different materials than the bit gage and the interior of the bit body. Thus, a bit body according to the present invention may include a hard, abrasion- and erosion-resistant material, such as tungsten carbide, on the crown thereof, and less expensive and tougher, more ductile materials, such as steel, within the interior of the bit body.
When a molten material is employed as the core material, the substantially hollow shell that comprises the crown of the drill bit is preferably infiltrated prior to forming the bit interior and the gage of the bit. As the molten core material is disposed within and adjacent to the substantially hollow shell, the binder with which the substantially hollow shell has been infiltrated, and which is exposed to the molten core material, preferably softens or melts and, thereby, mixes with or otherwise adheres to the core material to form a substantially integral structure. Alternatively, the molten core material may also be employed as a binder to infiltrate the particulate-based, substantially hollow shell substantially concurrently with disposal of the molten core material within and adjacent to the substantially hollow shell.
When the core material is particulate-based, the core material is preferably disposed within the substantially hollow shell and the bit gage mold prior to infiltration. The particulate core material and the particulate-based bit crown are then substantially integrally infiltrated with a binder. Thus, a substantially integral structure is formed.
Accordingly, the bit body of the present invention includes a particulate-based bit crown shell and an integral bit gage and bit interior secured to the bit crown shell.
A mold that may be employed to fabricate a bit body in accordance with the method of the present invention may include a soft, or conforming, section and an adjacent hard, rigid section. As discussed above, the soft, conforming section of the mold supports a preformed structure, such as a substantially hollow shell of a bit crown. The hard, rigid section of the mold is employed in combination with the preformed structure to define another structure, such as a bit gage, adjacent to the preformed structure. Upon definition of another structure by the hard, rigid section of the mold, the mold may be removed from the formed structure.
When such a mold is utilized to fabricate an earth-boring drill bit, the bit crown is disposed within the soft, conforming section of the mold so that the soft mold material substantially conforms to the shape of the exterior surface of the bit crown, including the various topographical features thereof. In assembling the soft, conforming section of the mold and the hard, rigid section of the mold, which comprises the bit gage mold, the hard, rigid section of the mold is disposed adjacent to the bit crown and the soft section of the mold. Thus, the hard, rigid section of the mold is preferably a substantially annular structure comprising a material, such as graphite or ceramic, that will withstand the temperatures and other conditions of disposing a molten material, such as a molten binder or molten core material, therein. Moreover, the interior of the hard, rigid section of the mold preferably includes relatively easily machinable features, such as forms for the gage pads and junk slots of the bit body.
Upon assembly of the soft, conforming section of the mold and the hard, rigid bit gage mold, the interior of the substantially hollow shell of the bit crown and the interior of the bit gage mold define a cavity. Mold inserts may be disposed within the cavity, as known in the art, to define various features of the bit body, including internal fluid courses, nozzle displacements, and topographical features of the bit body. Preferably, however, the nozzle displacements and topographical features of the bit body are defined during the layered-manufacture of the bit crown and by the bit gage mold.
Accordingly, the relatively complex topographical features of the bit crown may be substantially faithfully defined during the layered-manufacture of the bit crown, while the more easily defined and machined features, such as the gage pads, junk slots, and internal fluid courses of the drill bit, may be defined by the hard, rigid bit gage mold and by mold inserts.
Since layered-manufacturing processes are employed to fabricate only a shell of the bit crown and, thus, only a fraction of the entire bit body, the amount of time consumed by layered-manufacturing is reduced relative to that required when the entire bit body or an entire bit body shell is fabricated by layered-manufacturing processes.
Similarly, as the bit gage mold and mold inserts define larger, less complex features of the bit body, the bit gage mold and the mold inserts may be fabricated quickly relative to the amount of time that would otherwise be required to machine a mold that defines all of the features of the bit body. Moreover, the bit gage mold and mold inserts may be fabricated concurrently with the fabrication of the bit crown by layered manufacturing techniques.
Other features and advantages of the present invention will become apparent to those in of skill of the art through consideration of the ensuing description, the accompanying drawings, and the appended claims.